Illumination systems for office and commercial space normally require a certain standard of illumination, at a certain distance from the ceiling. Typically, in office buildings, the standard of illumination required is about 50 foot candles per square foot, at a distance of about six feet below the ceiling i.e., the level of a desk or table. Lighting systems today almost always employ fluorescent lighting tubes, which average approximately forty watts per tube in power consumption. Such lighting tubes are usually supported in rectangular boxes known as lighting troffers. In a large number of office and commercial buildings, such troffers are used in which two such tubes are present. Typically the troffers will be supported on a ceiling frame or grid structure, consisting of ceiling tees, defining a modular dimension of two feet by four feet. Typically the troffers will be two feet by four feet in dimensions, so as to simply rest on the ceiling tees. Depending upon the height of the ceiling and the level of illumination specified in a particular building, such lighting troffers may be provided in a variety of different numerical ratios or proportions, to the number of modules defined by the ceiling grid.
As is well known, such lighting troffers incorporate a so-called "ballast". The ballast is essentially a transformer which is required for reducing the incoming voltage, typically 120 volts, down to the voltage required for the typical lighting tube.
It is well known that such ballasts develop a certain amount of heat during operation. In addition, the lighting tubes themselves also generate heat. Such lighting tubes may be left on at least throughout all the working hours of a day, and in some cases are left on twenty-four hours a day. The heat generated within each troffer is usually simply dissipated within the ceiling space, above the ceiling grid.
It is also well known however, that the generation of such heat both by the tubes and by the ballast, tends to reduce the working life of both the tubes and the ballast. Certain forms of troffers in fact, provide for air circulation openings in order to disperse the heat away from the lighting troffer more rapidly.
The replacement of tubes and ballasts, as well as of course, the consumption of power to operate the lighting tubes themselves, therefore represents a significant cost in the operation of a building. The replacement of the ballasts in particular is a tiresome procedure, and occupies significant man-hours of time on behalf of maintenance personnel in a building.
In addition to all of these factors, the industry commonly arranges the wiring of such lighting troffers whereby one troffer is wired directly to the supply panel, carrying power from the power source. Adjacent lighting troffers are then wired back from the troffer connected to the power source, several troffers may be wired one after the other in this way. This system is well understood, and has been employed satisfactorily. However, it does impose certain restrictions on the type of wiring that may be used. Thus, depending upon the number of troffers that can be wired together, to a single power source, the cable from the original troffer to the power source, and all of the cables connecting to the connected troffer S, must all be of sufficient capacity to carry the voltage and current required to each of the troffers. In the vast majority of systems, the voltage supplied is the standard line voltage i.e. about 120 volts. In order to accommodate the wiring of several troffers together, to a single power troffer, it has been customary to employ a relatively heavy-duty wiring, typically number twelve gauge wiring, has been used throughout. Within each troffer however, since the effect of the ballast is to reduce the voltage supplied to the tubes themselves, wiring of a much lesser capacity may be employed.
At one time, it was the custom for electricians to actually run the wires from the panel to the first troffer and then connect to the connected troffers, simply using standard electrical connections consisting of baring the end of an electrical wire, bending it into a loop and fitting it around a screw. More recently, however, in order to reduce the man hours of trade persons involved at the actual building site, troffers have been made with plug-in connection systems, and wiring harnesses have been prepared in the factory, with plugs to connect to the various troffers. This system increases the factory labor input but decreases the on site trades person input, and thus in fact produces a net saving which is significant. However, since all of the wiring has to be heavy duty wiring, typically number twelve gauge wiring, the plugs have also had to be designed and specified to the same power requirements. This factor has tended to somewhat reduce the actual potential savings involved in the use of plug-in wiring harnesses.
As mentioned, all of these factors have been industry standard for many years. However, recent developments in the design and manufacture of the lighting tubes themselves, have resulted in the production of lighting tubes giving a somewhat more efficient lighting output, for the same expenditure of electrical energy. Since the illumination specifications in the majority of buildings have not materially changed over the years, it is clear that using the new tubes, illumination specifications equal to those previously required, can now be achieved, with a somewhat reduced power consumption.
Some slight advantage can be obtained simply by re-lamping existing troffers with the new lighting tubes, and a slightly greater lighting output would be achieved, than the same troffer using two of the old tubes. This factor would then mean that a slightly lower numerical ratio of troffers could be used over a given ceiling area. This is not, however, a simple matter of illumination directly below each lighting troffer. As the number of troffers in a given ceiling area is reduced, then the spread of illumination between any two adjacent troffers becomes a critical factor. If two adjacent troffers are spaced too far apart, then the illumination will tend to fall off, at a mid-point between the two troffers, to a point where it is unacceptable and below specifications. Accordingly, the obvious solution of simply replacing the old tubes with new tubes and reducing the number of troffers will produce little, if any advantage, and may result in the production of significant, undesirable variations in illumination from one area to another.
Another factor affected by the design of the new lighting tubes, is the design of the troffers themselves. In the past, the majority of lighting troffers were formed of sheet metal, which was simply painted white, or in some cases, was silvered in some way. Little, if any effort was made to provide any high degree of efficiency in the reflection of the light generated by the tubes. However, the new tubes that are now available, comprise cylindrical tubes, which are of significantly smaller diameter than the old style of tubes. It has now been found by experimentation, that by providing a reflector for each of the these new tubes, having a highly reflective surface, and by optimizing the shape of such reflector, that a significantly greater proportion of the light output of the new tubes can be reflected downwardly from the troffer and thus, provide useful illumination in the space beneath the troffer. This factor is, at least in part, due to the fact that the new tubes, are of lesser diameter than old tubes. This then results in a source of light which more closely approaches a "point" source of light, than did the old style larger diameter tubes. After careful development and testing, it has been found that the shape and reflective surface of a reflector can be optimized by using two pairs of curved reflective surfaces, namely a central pair and two side surfaces, and by placing the new smaller diameter tube as close as possible to the effective focal point of such an optimized reflector, that a significantly greater light output can be obtained, than could be obtained with prior art larger tubes.
A careful study of the situation in view of these factors, reveals that for example in a great many buildings, it will now be possible to obtain adequate lighting, using troffers with single, new, tubes and reflectors, to replace old troffers having two old style tubes. In the same way it becomes possible to use troffers having two of the new tubes and a reflector, to replace old troffers having four of the old tubes. The numerical arrangement of such smaller troffers in a ceiling would still of course, be dependent upon the required illumination at a certain level within the building. The new troffers, using new tubes and reflectors may produce up to fifty percent more illumination, for a given electrical consumption, than the old troffers using old tubes. It is thus, obvious that it will not be adequate to replace each old troffer with two tubes, with a new troffer with a single tube. There will have to be some increase in the number of new troffers holding the new tubes in order to produce the same illumination as was previously achieved using old troffers having the old tubes. However, the substitution of smaller new troffers for larger old troffers, while using the new tubes and reflectors, will produce a lighting plan in a building which will be more flexible and adaptable, and at the same time provide entirely adequate illumination, with, in fact, a less noticeable degree of variation in the space between two adjacent troffers.
However, if it was simply a matter of replacing the old troffers with two tubes with new troffers with a single tube, the greatest efficiencies available would not be achieved. This is because even with a lighting troffer using only a single tube, a ballast is still be required for each troffer. Thus although the troffers are smaller, the fact that a somewhat greater number of new troffers will be required to achieve the same overall lighting intensity, would apparently mean that there will be a greater number of ballasts in any given ceiling. This would tend to mitigate against any significant savings in capital costs in particular, and also in maintenance for replacement costs of burnt-out ballasts and the like.
Similarly, if it were simply a matter of replacing the old lighting troffers, using two old tubes with new lighting troffers using a single new tube, and the same prior art wiring system were used, then the fact that each of the new lighting troffers would have to be connected by means of heavy gauge cable, with or without plug-type harnesses, would again tend to reduce the efficiencies, and increase the cost of changing over to such a new system. In spite of all of these complex factors, the advantages to be gained by the use of the new troffers and tubes will in almost all cases warrant the use of such new troffer and tube illumination systems in new construction. However, there are clearly a very large number of buildings already fitted with illumination systems using the old troffers and tubes and it would be highly desirable if an illumination system could be achieved in which the savings were so significant that they would warrant retrofitting existing buildings with new troffers and tubes.
Provided such an energy efficient illumination system could be achieved at an acceptable capital cost, then there would be a substantial benefit to developers of new buildings, and a significant benefit to the owners and operators and of old and existing buildings.
More significantly, however, there would be a substantial reduction in the demand for electrical power, and this would enable electrical utility authorities to slow down the development of new power generation equipment, and to possibly reduce to a significant degree the energy consumption presently expended on the generation of electricity required for illumination. Utilities will, in many cases, offer rebates to customers to encourage the upgrading of old buildings, in this case.
Clearly, it is desirable to provide an illumination system wherein use may be made of the newer high-efficiency troffers and lighting tubes, and at the same time, reductions may be made in installation costs, and furthermore, reductions may be made in the frequency of tube replacement, and ballast maintenance and the like, with a view to permitting such high-efficiency troffers and lighting tubes to be used both in new construction, and also to show sufficient improvement in efficiencies, so that owners of existing buildings will experience significant savings over time, by retrofitting their buildings with the new troffers and lighting tubes.